1. Field of the Invention
This invention relates to isocyanate compositions and is more particularly concerned with polymethylene polyphenyl polyisocyanates having improved reactivity and storage stability.
It is well recognized in the art that the presence of free hydrogen chloride, and a wide variety of by-products containing hydrolyzable chloride, produced during the preparation of polyisocyanates by phosgenation of the corresponding amines, has an adverse effect on the rate of reaction of said polyisocyanates with active hydrogen-containing materials such as polyols. This is particularly so in the case of polymethylene polyphenyl polyisocyanates, i.e., the products derived by phosgenation of the mixture of polyamines obtained in the acid condensation of aniline and formaldehyde.
Various methods of adjusting the reactivity and or lowering the hydrolyzable chloride content of such polyisocyanates have been described; see, for example, U.S. Pat. Nos. 3,793,362 and 3,912,600 and the prior art which is discussed therein. We have now found that the reactivity of the above type of polyisocyanates can be increased, and the increased level of activity can be maintained over a prolonged period of storage, by use of very minor amounts of a class of compounds not hitherto recognized as useful for this purpose. Further, the use of these compounds to increase reactivity of the polyisocyanate does not affect adversely the other desirable properties of the polyisocyanate or the properties of the products derived therefrom by reaction with active-hydrogen containing compounds.
Certain members of the above class of compounds, namely oxazolines carrying substituents in the 2-position alone or in the 2- and 4-positions simultaneously, have been shown to be catalysts in the reaction of polyisocyanates with polyols; see U.S. Pat. No. 3,914,189. However, it has not previously been recognized that these compounds, when incorporated into isocyanates in lower amounts than those required for catalysis in accordance with the above reference, would enhance and stabilize reactivity of the isocyanate.